<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            width: 300px;
            height: 300px;
        }
    </style>
</head>
<body>
    <div></div>
    <script>
        function getRandomColor(flag = true) {
            if (flag) {
                let str = '#'
                let arr = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f']
                for (let i = 1; i <= 6; i++) {
                    let random = Math.floor(Math.random() * arr.length)
                    str += arr[random]
                }
                return str
            } else {
                let r = Math.floor(Math.random() * 256)
                let g = Math.floor(Math.random() * 256)
                let b = Math.floor(Math.random() * 256)
                return `rgb(${r}, ${g}, ${b})`
            }
        }
        console.log(getRandomColor(false))
        console.log(getRandomColor(true))
        console.log(getRandomColor())
        const div = document.querySelector('div')
        div.style.backgroundColor = getRandomColor()
    </script>
</body>
</html>